Typical bicycles are driven by crank systems, which utilize unidirectional rotational movement to propel the bicycle drive wheel. Such directional rotational movement results in a varying torque induced by a primarily downward foot pressure from near zero to a maximum and back again to zero for each half revolution. This motion is necessitated by the conventional crank design, which includes a continuous chain that is received around a crank and a sprocket. Conventional bicycles also include shifting mechanisms, which adjust the drive ratio between the crank and the sprocket by controllably locating the chain about selected sprockets of different diameters. These conventional crank driven bicycles, with their varying torque, are difficult or impossible to ride for those with certain physical disabilities such as a person with only one leg, a person having one leg weaker than the other, a person having limited range of motion, etc.
One possible solution to assist the physically disabled in riding bicycles includes the lever driven bicycle, which has been designed to replace the conventional drive with oscillating displacement of the lever. Such lever driven bicycles utilize a dual lever arrangement in which each lever oscillates individually as propelled by each leg of the rider. One example of a lever driven bicycle is disclosed in U.S. Pat. No. 3,039,790 to Trott. Lever driven bicycles have also been designed with shifting mechanisms which allow for manual control of the drive ratio between the lever and the drive wheel. For example, U.S. Pat. No. 3,834,733 to Harris and U.S. Pat. No. 4,421,334 to Efros both disclose lever driven bicycles having shifter arrangements which allow the rider to manually adjust the drive ratio between the lever and the drive wheel. U.S. Pat. No. 5,988,662 to Staehlin also describes a lever driven bicycle configured for manual adjustment of a shifting mechanism.
The oscillating motion of a lever driven bicycle may be preferable to a physically disabled rider because of the substantially constant torque and less cumbersome linear movement required to propel the bicycle. However, lever driven bicycles to date still do not produce the efficient drive and ease of power application required by many people with physical disabilities. Further, previous lever driven bicycles may require that adjustments to a drive ratio of each lever be made separately and independently. The separate adjustment configuration, however, may render it difficult for a rider to balance the drive ratios of the levers without extensively monitoring the settings. Further, previous lever driven bicycles lack means to insure that drive ratio adjustments are made while the drive wheel is rotating, which has been found to be safer and more efficient than making adjustments while the drive wheel is stationary. In light of the foregoing there is a need for an improved lever driven bicycle that allows for easier adjustment of the drive ratios of the levers, as well as for addressing the needs of the physically disabled and the frail elderly.
The present disclosure is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.